The present invention relates to an oil separator for de-oiling crankcase ventilation gases of an internal combustion engine wherein the oil separator comprises at least one cyclone encompassing a gas inlet connected to the crankcase of the internal combustion engine, a gas outlet connected to the air suction passage of the internal combustion engine, and an oil outlet connected to the crankcase sump of the internal combustion engine, wherein the gas outlet, as a submerged pipe, projects through a lid into the cyclone interior with the lid closing the cyclone at the top.
An oil separator of the kind mentioned above, e.g., is known from the DE 42 14 324 C2. The submerged pipe serving as a gas outlet in this oil separator is continued as a gas pipe above the lid closing the cyclone on top, with the gas pipe being extended to the air suction passage of the internal combustion engine. It is considered to be a disadvantage of this known oil separator that during operation remaining oil particles are carried in the direction of the gas outlet which leads to an thick oil deposit at the inner surface of the gas outlet. When a certain thickness of this oil deposit is reached, and when sufficiently large gas flow velocities occur, some of this oil may again enter the clean gas flow. The oil particles carried by the clean gas flow necessarily enter the air suction passage of the internal combustion engine which is non-desired as hereby the mix ratio for the internal combustion engine is influenced in a negative manner.
Therefore it is an object of the present invention to provide an oil separator of the kind mentioned above which avoids the disadvantages mentioned and whereby it is ensured that no additional oil particles can be carried by the clean gas flow.
According to the invention this object is attained by an oil separator of the kind mentioned above which is characterized in that a gas duct section is provided above the gas outlet on top of the lid with the gas duct section comprising a cross-section enlarged to at least double size, and that an oil drain passage is guided from this section downwards to the oil outlet or the crankcase sump.
With the design of the oil separator according to the invention oil droplets which are eventually present in the gas flowing from the cyclone through the gas outlet, are precipitated in the area of the gas pipe section which is enlarged in the diameter thereof and cling to the surfaces thereof, and flow to the oil drain passage under the influence of gravity, with the oil being guided either directly to the crankcase sump of the internal combustion engine or firstly to the oil drain and from there together with the oil separated in the cyclone to the crankcase sump of the internal combustion engine. In this manner the oil separation rate is particularly high, and neither oil mist nor occasionally larger oil drops get into the air suction passage of the internal combustion engine. This has a positive effect on the exhaust values of the internal combustion engine, and minimizes the oil consumption of the internal combustion engine such that the oil has to be less.
In order to avoid a non-desired gas flow from bottom to the top through the oil drain passage, it is provided that the lower end of the oil drain passage is designed with a siphon or a check valve.
In a further embodiment of the oil separator it is provided that the submerged pipe ends shortly above the lid, that the oil drain passage begins from the top side of the lid, and that for forming the gas duct section, a bell-shaped or hopper-shaped hood is arranged above the lid with the hood comprising a diameter at its bottom which at least equals that of the lid, with the hood having a narrower open end on top which is designed as a connection piece to be connected to the suction passage of the internal combustion engine. With this embodiment of the oil separator on the one hand the desired function is attained, and on the other hand a simple construction which enables a construction of the oil separator from relatively few and non-complicated parts.
In order to guarantee a dedicated and effective oil drain from the area on top of the lid, it is provided that an annular indentation extends around the lid, or that the lid comprises an indentation and/or a slope at its top, and that the oil drain passage begins in the indentation or at the lowest point of the slope. By this means the oil is collected and drained, wherein it is guaranteed that it will not get into the area of high gas flow velocities where it may be carried away by the flowing gas.
Regarding the submerged pipe it is preferably provided that the submerged pipe is designed with a cross-section which is enlarged in the gas flow direction, and is preferably conical. On the one hand, by this design a high oil separation rate of the cyclone is attained, and on the other hand, a reduction of the gas flow velocity at the upper end of the submerged pipe occurs which is favorable for the separation of remaining oil above the submerged pipe in the gas pipe section with the enlarged cross-section.
Further, it is preferably provided that the oil outlet is designed with an oil collection hopper arranged below the cyclone, and that the lower end of the oil drain passage opens into the oil collection hopper. By this means, in a simple way, a collection of the two oil streams from the oil outlet positioned at the lower end of the cyclone, and of the oil drain passage in the vicinity thereof, is attained. The further return flow up to the crankcase sump of the internal combustion engine is then attained by a common and single oil pipe.
The oil separator according to the DE 42 14 324 C2 mentioned above comprises a single cyclone for separating the oil from the crankcase ventilation gas. Deviating from this construction it may be prudent for improving the efficiency of the oil separator, in different and fluctuating working conditions of the internal combustion engine, to design the oil separator with two or more cyclones. For such an embodiment the present invention preferably provides that the hood overlaps the lids and the submerged pipes of all cyclones, and that a single oil drain passage is provided. In this manner a compact design, with few and relatively simply shaped single parts of the oil separator, is attained, keeping the manufacturing and assembly costs low.